looks great 8)
The only thing i'd say though is that surface agitation removes CO2 from the water so diffusing it through a HOB is prob not the most efficient way of getting the CO2 into the tank. I've tried feeding the CO2 into my external cannister filter but this resulted in an air (or in this case a CO2) lock in the filter. At the moment I have my CO2 pipe bubbling under the inlet of a 360l/hr powerhead. This smashes up the bubbles nicely. I've also got the outlet pointing down which drives the tiny CO2 bubbles to the bottom of the tank givng them longer to dissolve before they reach the surface.